ZnO based varistors are today frequently used for surge arresters. In order to obtain a better behavior of that piece of equipment, it is very important to know the continuous voltage limits accepted. This goal could be achieved only by making some experiments to evaluate the thermal limits of a certain varistor. This paper presents some original experiments made by the authors at the “Genie Electrique” Laboratory of the “Paul Sabatier” University in Toulouse, France. These experiments are original because they are taking in consideration the environmental temperature too, and they provide technical solutions for an optimal service of that equipment.

Keywords: Functional limits, ZnO varistor, Surge-arrester.